1. Field of the Invention
The present invention relates to a light emitting device, a display device and a method of manufacturing the display device.
2. Description of the Related Art
In recent years, light emitting devices (hereinafter referred to as “LEDs” for short), and organic light emitting diodes (hereinafter referred to as “OLEDs” for short) have been in widespread use as light emitting elements. Also, the LEDs and the OLEDs are widely utilized in the various fields of a light emitting device constituting lighting equipment, a display device called a flat panel display, and the like.
In the case where the light emitting device, the display device or the like is constituted by the light emitting element such as the OLED or the LED, it is demanded that light extraction is efficiently carried out. The reason for this is because the low light extraction efficiency leads to that an amount of actual luminance in the light emitting element is not effectively utilized, which triggers a large loss in terms of power consumption or the like.
For this reason, it is proposed to enhance the light extraction efficiency by using a micro-prism, a micro-lens, a concave mirror or the like in the light emitting device, the display device or the like using the OLED, the LED or the like. The technical propose, for example, is disclosed in Japanese Patent Laid-open Nos. 2003-77648 and 2002-184567.
In addition, recently, an example is also reported in which a structure of a compound parabolic concentrator (hereinafter referred to as “a CPC” for short) used as a concentrator for use in a solar cell is applied to a self light emitting device such as an organic EL element. This report, for example, is disclosed in Japanese Patent Laid-open No. 2005-531102.
Here, the CPC will be described in brief.
The CPC is devised for the purpose of efficiently guiding a light to a solar cell. The feature of the CPC is that a light reflected by a reflecting surface is necessarily directed toward a surface of a solar cell. Also, the CPC, as shown as its name, is a compound concave mirror using a part of a parabolic surface.
For details, as shown in FIG. 14A, a parabolic surface has a property that incident parallel rays of light are collected at one point (focal point). Here, it is considered the case that a lamination state of a layer made of a translucent material having a refractive index of N and an air layer contacting an interface between them as shown in FIG. 14B. When a symmetric axis of a parabolic surface formed on the translucent material layer is inclined at a critical angle having a view angle of θ=sin−1(1/N) between the layers, even if a light is made incident at a high angle near 90° from the side of the air layer, as shown in FIG. 14C, the light concerned necessarily passes through a line segment joining a focal point F of the parabolic surface and a point A on the parabolic surface. By utilizing these properties, a rotationally-symmetric body which is obtained such that a part of the parabolic surface is rotated with a central axis being set up at a middle point of a line segment FA as shown in FIG. 14D is a shape called the CPC. Thus, placing a solar cell on a surface containing the line segment FA allows the effective utilization of the light.
When such a structure of the CPC is applied with the surface of the solar cell as an emission surface, a very efficient reflecting mirror is obtained because a light emitted from the emission surface is necessarily extracted to the outside.